Basement Wall

UNIVERSITI TEKNOLOGI MALAYSIA

PSZ 19:16 (Pind.1/07)

DECLARATION OF THESIS / POST GRADUATE PROJECT PAPER AND COPYRIGHT Author’s full name

: MEGAT ZAHARI BIN MEGAT JAAFAR

Date of birth

: 20th April 1966

Title

: Semi Top Down and Bottom Up Construction Work in

Deep Basement of Tall Building in Kuala Lumpur. Academic Session : 2009/2010 I declared that this thesis is classified as :

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(Contains confidential information under the Official Secret Act 1972)*

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660420-02-5567 NEW IC NO.

ASSOCIATE PROFESSOR DR. A.AZIZ SAIM

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If the thesis is CONFIDENTIAL or RESTRICTED, please attach with the letter from the organization with period and reasons for confidentiality or restriction

“ I hereby declare that I have read this project report and in my opinion this project report is sufficient in terms of scope and quality for the award of the degree of Master of Engineering (Civil-Structure)”

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Associate Professor Dr. A.Aziz Saim

Date

:

SEMI TOP DOWN AND BOTTOM UP CONSTRUCTION WORK IN DEEP BASEMENT OF TALL BUILDING IN KUALA LUMPUR.

MEGAT ZAHARI BIN MEGAT JAAFAR

A project report submitted in partial fulfilment of the requirements for the award of the degree of Master of Engineering (Civil-Structure)

Faculty of Civil Engineering Universiti Teknologi Malaysia

NOVEMBER 2009

ii

I declare that this project report entitled “Semi Top Down and Bottom Up Construction Work in Deep Basement of Tall Building in Kuala Lumpur” is the result of my own research except as cited in the references. The project report has not been accepted for any degree and this is not concurrently submitted in candidature of any degree.

Signature

:

………………………………….…

Name

:

Megat Zahari Bin Megat Jaafar

Date

:

iii

Special dedication to my beloved wife (Noorleha Lee Jung-hee) who has fully given encouragement and moral support towards accomplishment my study and to my dearest daughter (Wan Noorlily).

……….. for everlasting love and cares………

iv

ACKNOWLEDGEMENT

I would like to thank Associate Professor Dr.A.Aziz Saim of the Faculty of Civil Engineering, Universiti Teknologi Malaysia who has reviewed and given commitments, comprehensive and generous advice towards accomplishment of this project report. Great thank to all personnel of both projects who have contributed thoughts and information during my field study.

v

ABSTRACT

This project report is to present underground basements construction work in tall building constructed with bottom up method and semi top down method. Bottom up method is normally carried out in area with fewer plant facilities to operate. Semi top down method is carried out in urban area with compact surround area to reduce construction period and cost. Three floors underground basement founded on same type underground limestone from two projects of 30-storey building are investigated. The excavation for both basement substructures is varied from 14m to 18m below existing ground level. The work methodology in the basement construction work is presented. Excavation works, slope stabilization, retaining systems, site instrumentations and under ground water table are those parameters influenced in substructure works. All the parameters from both methods are compiled during substructure work then assessed and evaluated in view of technical aspect. Contrary to bottom up method, in semi top down method, the retaining wall system and pre installed temporary stanchion are required, however shot-crete in slope stabilization, steel strutting system and earth backfilling are eliminated.

It appears that in basements works using semi top down method has

offered more advantages compare with bottom up method in view of shorter construction period and cost effective. The suggestions proposed for preliminary study in three floors basement work are rate completion time are 16.3m2/day and 13.2m2/day and for construction cost at sub-contractor price are RM1,556.92/m2 and RM1,758.76/m2 for semi top down method and bottom up method respectively.

vi

ABSTRAK

Lapuran projek ini mengupaskan kerja-kerja besmen bawah tanah dalam pembinaan bangunan tinggi mengunakan cara kerja bawah ke atas dan cara kerja separa atas ke bawah. Cara kerja bawah ke atas dijalankan di kawasan yang tidak memerlukan penggunaan banyak jentera. Cara kerja separa atas ke bawah pula dijalankan di kawasan yang padat sekelilingnya dengan mengambilkira penjimatan kos dan masa pembinaan. Pembinaan dua bangunan setinggi 30 tingkat dengan tiga besmen bawah-tanah di atas tanah batu-kapur dikajisiasat. Kerja-kerja mengorek tanah untuk sub-struktur di keduadua besmen bangunan tersebut adalah di sekitar 14m sehingga 18m kedalamannya dari aras sediaada. Tata kerja dalam pembinaan besmen tersebut dibentangkan. Kerja-kerja pengorekan tanah, kesetabilan cerun, sistem penghadangan, alat-alat pengukuran tapak bina dan aras air bawah tanah adalah pembolehubah yang mempengaruhi kerja-kerja substruktur. Semua pembolehubah dari kedua-dua cara kerja disusunkan semasa kerjakerja substruktur, selepas itu ditentukan dan dinilaikan dari sudut teknikal. Berbeza dari cara kerja bawah ke atas, didapati cara kerja separa atas ke bawah memerlukan sistem dinding penghadang dan tiang pasang siap, walaubagaimana pun pelindungan shot crete dalam kesetabilan cerun, sistem besi jermang sadak (steel strutting system) dan timbus balik tanah tidak diperlukan. Kerja-kerja besmen menggunakan cara kerja separa atas ke bawah didapati memberi kelebihan berbandingkan cara kerja bawah ke atas dari sudut masa pembinaan yang singkat dan penjimatan kos kerja. Cadangan yang diutarakan untuk kajian permulaan dalam pembinaan tiga besmen bawahtanah adalah kadar masa pembinaan ialah 16.3m2/hari dan kadar harga subkontraktor ialah RM 1,556.92/m2 bagi cara kerja separa atas ke bawah. Manakala bagi pembinaan mengikut cara kerja bawah ke atas, kadar masa pembinaan ialah 13.2m2/hari dan kadar harga subkontraktor is RM 1,758.76/m2

vii

TABLE OF CONTENTS

CHAPTER

1

2

TITLE

PAGE

DECLARATION

ii

DEDICATION

iii

ACKNOWLEDGEMENT

iv

ABSTRACT

v

ABSTRAK

vi

TABLE OF CONTENTS

vii

LIST OF TABLES

x

LIST OF FIGURES

xi

CHAPTER 1 - Introduction 1.1

Introduction

1

1.2

Problem Statement

3

1.3

Aim and Objective

3

1.4

Scope of Project Study

4

CHAPTER 2 - Construction Of Basement In Tall Building 2.1

Introduction

5

2.1.1

Soil Investigation

6

2.1.2

Ground Water

8

2.1.3

Raft and Piled Raft

9

2.1.4

Retaining Wall

10

viii 2.2

3

4

5

Criteria in Deep Basement Work

11

2.2.1

Dilapidation Survey of Adjacent Structures

12

2.2.2

Instrumentation and Monitoring Program

13

2.2.3

Supervision and Construction Control

15

2.3

Bottom Up Method in Deep Basement Work

18

2.4

Semi Top Down Method in Deep Basement Work

20

CHAPTER 3 - Methodology 3.1

Introduction

23

3.2

Project Study Case

23

CHAPTER 4 – Project 1: Bottom Up Method in Deep Basement Work 4.1

Introduction

26

4.2

Substructure Construction Planning Sequences

28

4.3

Erection of Contiguous Bored Pile

31

4.4

Foundation Bored Pile

32

4.5

Earth Excavation

33

4.6

Instrumentation and Monitoring

36

4.7

Raft Basement Construction

38

4.8

Erection of Strutting and Bracing

41

4.9

Construction Basement Floors to Ground Floor

44

4.10

Backfilling with Suitable Material

45

CHAPTER 5 – Project 2 : Semi Top Down Method in Deep Basement Work 5.1

Introduction

48

5.2

Basement Construction Planning Sequences

50

5.3

Contiguous Bored Pile

51

5.4

Foundation Bored Pile

53

5.5

Pre-installed Column Stanchion

56

5.6

Top Down Work

57

5.7

Floor Casting and Top Down Work

60

ix 5.8

6

7

Foundation Base Casting and Bottom Up Work

62

CHAPTER 6 – Data Analysis 6.1

Introduction

66

6.2

Parameter Activities

67

6.3

Design Parameter

67

6.4

Time and Cost Completion Work

72

CHAPTER 7 - Conclusion and Suggestion 7.1

Introduction

77

7.2

Conclusion

77

7.3

Suggestion

78

REFERENCES

80

x

LIST OF TABLES

TABLE NO.

TITLE

PAGE

2.1

Common types of instrument for basement construction works

14

6.1

Parameter in bottom up underground basement work

in

69

6.2

Parameter in semi top down method in underground basement work

70

6.3

Parameter designs influenced in bottom up and semi top down method of underground basement work

71

6.4

Actual work completion of bottom up method for Project 1

75

6.5

Actual work completion of semi top down method for Project 2

76

excavation

method

xi

LIST OF FIGURES

FIGURE NO.

TITLE

PAGE

1.1

Tall buildings in Kuala Lumpur

2

2.1

Typical arrangement of soil investigation using percussion borins (a) percussion boring rig, (b) boring rod and chisel

7

2.2

Typical sump arrangement

8

2.3

Propped piled wall (a) stage 1, (b) final stage

10

2.4

Plan view of contiguous bored pile with skin wall

11

2.5

Open excavation with slope protection

15

2.6

Open excavation with braced wall (a) internally strutting to wall, (b) wall with ground anchor

16

2.7

Closed excavation with braced wall in full top down method

16

2.8

Semi top down work

17

2.9

Open excavation in deep basement work

18

2.10

Bottom up method in deep basement

19

2.11

Lateral force acting in deep basement

20

2.12

Semi top down method in deep basement

21

xii 3.1

Methodology flowchart of project study

24

4.1

Layout plan of retaining system

27

4.2

Site observation method chart

29

4.3

Basement work planning in stages

30

4.4

Contiguous bored pile at perimeter site boundary

31

4.5

Foundation bored pile in dry condition

32

4.6

Excavation work in stages

33

4.7

Exposed slope with shotcrete

34

4.8

Progress of excavation work

35

4.9

Proper trimming work at base

36

4.10

Typical installation detail for inclinometers

37

4.11

Installation inclinometer behind wallperimeter bored pile

38

4.12

Rebar installation for raft base in progress

39

4.13

Raft foundation concreting work is being in progress

40

4.14

Raft foundation curing with polystyrene sheet cover on top surface

41

4.15

Typical installation of temporary inclined steel strutting with reinforced concrete corbel support integrated to raft foundation

42

4.16

Temporary strutting structure and excavation work in progress

43

4.17

Temporary strutting structure to support retaining wall (sheet pile and contiguous bored pile)

43

4.18

Basement floor in sequences casting work

44

xiii 4.19

Basement work at construction joint

45

4.20

Gap between basement wall and open slope

46

4.21

Backfilling to required level

47

5.1

Layout plan of semi top down site

49

5.2

Basement work planning in stages

50

5.3

Contiguous bored pile work in progress

52

5.4

Cut off contiguous bored pile to required level

53

5.5

Soil investigation (SI) works are being in progress at each column position

54

5.6

Lowering down rebar cage in wet hole bored pile

55

5.7

Pre-installed steel stanchion column in bored pile

56

5.8

Ground floor formwork in progress

57

5.9

Top down work in progress

58

5.10

Excavation work to expose pre-installed steel stanchion column

59

5.11

Excavation work to formation level carried out at center of building downward

60

5.12

Top view of top down work at perimeter building

61

5.13

Bottom up work at center of building

62

5.14

Bottom up area with basement raft work in progress

63

5.15

Bottom up work for center building structure

64

6.1

Actual cost and time completion for semi top down method and bottom up method without pile foundation

73

CHAPTER 1

INTRODUCTION

1.1

Introduction

In Malaysia, tall buildings with deep basements have been extensively constructed mainly in the expensive and congested urban area. Basements effectively serve as underground space for car park and other usage in extensive scheme. The excavation of the deep basement requires much attention of structural and geotechnical engineers as well as contractor itself. The considerations involved in design and planning contributed to safety and economical aspect which should be emphasized at early stage. The execution of the deep basement construction work can be either carried out with method of bottom up or top down, however it is subject to site local geology condition and location of the building itself. The hybrid of both methods which is called semi top down method may look more viable to give influences in saving of both time and economical construction aspect.

In Kuala Lumpur area, as metropolitan city, development of tall building with underground basement rapidly being in progress recently, refer Figure 1.1. Demand on

2 luxurious standard living in town area with ease infrastructure has caused land usage is fully utilized. The development gives challenging to engineers and contractors to think intensively in designing and method of construction while maintaining client objectives to suit with functional of building itself. Based on local experience, construction of basement required more attention in economical aspect in finding accurate method to construct deep basement in safely manner.

Figure 1.1 : Tall buildings in Kuala Lumpur

3 1.2

Problem Statement

In construction of deep basements, the major concerned is safety and economical aspect. This matter is not only implies to project itself but also influence to surround existing building as well. Safety is mainly influenced by proper sequence activity in construction system which being implementing at the present of time. Economical is cost effective contributes to move the construction activity influenced by operation and monitoring activity. Settlement in soil contributed to ground movement is due to excavation, presence of ground water, vibration in piling works, stability system in bracing and strutting as well as others activity in basement construction works. The proper knowledge of sequence activity in excavation work executed plays important role to eliminate such consequence defects to existing adjacent structures or building. In cost estimating of underground structures, methodology of basement construction work, cost operation and time completion contributed in many type of construction method. In each method, there are certain limits influenced bound with the pros and cons of the system activity. Reviewing past project is able to give guideline decision to support estimation cost and time analysis for basement construction works.

1.3

Aim and Objective

The aim of the project study is to get comparison sequence activity, time and cost completion in basement work in tall building executed using two types deep basement construction method i.e (a) Bottom Up Construction Method and, (b) Semi Top Down Construction Method.

4 Through these two basement construction methods, the objectives of this project study are encompassed in:i.

Investigation of sequence activity in construction basement work of tall building.

ii.

1.4

Comparison in cost and time construction basement work of tall building.

Scope of Project Study

In capturing the above aim and objectives, field investigation is to be carried out from two selected tall building projects in Kuala Lumpur area which are:(i) Project 1:One (1) block 30-storey building with 3 floors basement at Jalan Ampang, Kuala Lumpur which basement work is carried out with Bottom Up Method, and (ii) Project 2:One (1) block 30-storey building with 3 floors basement at Jalan Tuanku Abdul Rahman, Kuala Lumpur which basement work is carried out with Semi Top Down Method Project 2 is commenced after one year late from Project 1. Both projects are founded on similar underground Kenny Hill Formation underlain by Kuala Lumpur Limestone.

CHAPTER 2

CONSTRUCTION OF BASEMENT IN TALL BUILDING

2.1

Introduction

Construction of basement in tall building is expensive due to nature of soil condition and ground water problems. The substructure basements are designed and produced by taking considering underground earth, water pressure and all vertical loads. The method of construction should be well planned and analysed in safety manner and economical aspect during preliminary stages of development work. Most of the people who work with underground project consider that a study of the past projects can provide some general idea as to trends in the future marketplace cost of the underground cost [1].

In engineering aspect, the excavation will induce stresses in the ground mass around the excavation changes. The most common changes in stresses in the retained side are the stresses relieve on the excavation face resulting in horizontal ground movement and follows by vertical movement for equilibrium. It increases vertical stress due to

6 lowering water table resulting in both immediate and consolidation settlement of the ground. Ground settlement due to soil movement is observed influencing towards defect such as cracks to non-suspended slab [2] and other main structure element of surround existing building when new construction of underground basement takes place nearby. Improper sequence of excavation is contributed preliminary failure in collapse to adjacent property [3].

Contractually, substructure construction integrated with temporary support system shall be the contractor’s responsibility not withstanding any suggestions given by the consultant engineer who may reject the use of any system he seems unsafe. It is imperative that basic principle of design and construction should be fully understood by all directly concerned and particularly by the resident engineer and the contractor’s site staff. The lack of communication between concerned parties can lead to misunderstanding that could have serious consequences.

Generally, basement construction work mainly influenced by (a) soil investigation, (b) ground water, (c) foundation system – raft and piled raft and, (d) retaining wall

2.1.1

Soil Investigation

Soil investigation (SI) is required to be thoroughly carried out in tall building work. Basically, it is to get information of subsoil profile with respect to subsoil properties, shear strength and ground water condition. The principal objects [4] of the investigation are; (a) to determine the sequence, thickness and lateral extent of the soil strata and, where appropriate, the level of bedrock; (b) to obtain representative samples

7 of the soil (and rock) for identification and classification and, if necessary for use in laboratory tests to determine relevant soil parameter; (c) to identify the groundwater conditions.

SI is executed with a few methods [5] such as (a) trials pits, (b) hand auger borings, mechanical auger borings, (d) light cable percussion borings, (e) rotary open hole drilling, (f) wash borings, (g) wash probings, (h) dynamic cone penetration tests, (i) static cone penetration tests, (j) vane shear tests, (k) pressuremeter tests, (l) dilatometer tests and (m) plate bearing tests. Typical arrangement of SI using percussion boring is shown in Figure 2.1

Figure 2.1 [4]

: Typical arrangement of soil investigation using percussion borings (a) percussion boring rig, (b) boring rod and chisel

8 2.1.2

Ground Water

In order to carry out construction work below surface levels it is normally necessary for the working area to be reasonably free from standing water. The water flow must be either be blocked or carried away from the area. In selecting the proper method of dealing with ground water it is influenced by the type of soil height of water table, the depth of excavation and its shape. The purpose of de-watering is to lower the water table in the vicinity of an excavation to provide a relatively dry and stable working area. Water can be removed by pumping, isolated from the works by providing a barrier or drainage to a sump. Pumping from well/sump positioned outside the excavation boundary is usually preferred technique. The system of pumping from an open sump (Figure 2.2) is popular because the cost installation and maintenance of the equipment are relatively low compared to those for wells, and because the system is applicable to most soils [6].

Figure 2.2 [6] : Typical sump arrangement

9 2.1.3

Raft and Piled Raft

The chief function of a raft is to spread the building load over as great an area of ground as possible and thus reduce the bearing pressure to minimum. Raft provides a degree of rigidity that reduces differential movements in the superstructures. The settlement of a raft foundation does not depend on the weight of the building supports. Rather settlement depends on the difference between this weight and the weight of the soil that is removed prior the construction of the raft, provided the heave produced by the inconsequential. A raft can be built at a sufficient depth so that the weight of soil removed equals the weight of the building. Such rafts are referred to as buoyancy, compensated, floating or semi-floating foundation. The success of this type of foundation structure in overcoming difficult soil conditions has led to the use of deep raft and rigid frame basements for high buildings on clay soils.

Piled rafts [7] are used as a means of supporting tall buildings on a various types of soil. It would appear that the basement has a marked influence on the load displacement within a piled raft foundation. During the initial stages of construction, up lift forces resulting from the removal of soil can induce initial pressures on the base of a raft, together with tensile forces in the piles. Subsequent downward loading imposed by the structure slowly increases contact pressures and gives rise to a comparatively rapid build-up in compressive pile loads. The load distribution between the piles and the raft at any stage of construction depends on the ration of uplift force to vertical structural load. The long-term effect of consolidation is to increase the load carried by the piles and to decrease the raft contact pressures.

10 2.1.4

Retaining wall

Deep basement work frequently shoring. The choice of method depends upon technical factors. There are such as depth of the basement foundation, the available space, the nature and permeability of the soil, the depth of water table and economic considerations related to the period excavation must be left open, the availability of labour, plant and materials and the construction program. The cheapest method is to prop from the base of the excavation as shown in Fig 2.3 [6]. It is obviously can be progressively carried out as the excavation is deepened, if excessive cantilevering is to be avoided.

Figure 2.3 [6] : Propped piled wall (a) Stage 1, (b) Final Stage

11 Cost of shoring can be reduced when support system is designed as part of permanent works. Method involved the use of in situ bored pile cast to form a continuous wall. The row contiguous bore pile could be given a facing of reinforced concrete wall (skin wall) to improve of the surface appearance and water tight feature, refer Figure 2.4.

Figure 2.4 [6] : Plan view of contiguous bored pile with skin wall

2.2

Criteria in Deep Basement Work

The common selections criteria for deep basement subject to retaining wall type and support system [2] made usually on the basis of the followings:a. Foundation of adjacent properties and services, b. Designed limits on wall and retained ground movements c. Subsoil conditions and ground water level d. Working space requirement and site constraints e. Cost and time in construction f. Flexibility of the layout of the permanent works g. Local experience and availability of construction plant h. Maintenance of the wall and support system in permanent condition.

12 Based on the above criteria, the construction of deep basement apparently required involvement of design engineer, geotechnical engineer together with contractor hand in hand closely supervise the construction at site. The monitoring work at site is to review the performance of retaining structure and compare to design requirement and predictions. The necessary action in immediate time is solution to ensure the occurrence of critical limit state like large displacement of wall causing damage to nearby structures or services eliminated.

There are three major considerations being taken during construction deep basement [7] work in Malaysia, such as dilapidation survey of adjacent structures, instrumentation and monitoring program and supervision and construction control.

2.2.1

Dilapidation Survey of Adjacent Structures

In Malaysia, for deep excavation work, the dilapidation survey of adjacent properties is necessary to prevent unnecessary contractual conflict or even lawsuit. Dilapidation survey also forms part of the requirement by local authorities and serves as reference report in lawsuit. It should be carried out prior to any construction activities at the site.

During the excavation, the earth movement is expected. It induces stresses in both vertical and horizontal soil properties towards influenced defect to adjacent properties as well. The survey should be thoroughly carried out, with owner permission, in all angles at various locations at external and internal structure of the adjacent properties.

13 Photographs should be taken together with the measuring equipments and included in report.

2.2.2

Instrumentation and Monitoring Program

Instrumentation plays an important role in the underground basement construction activities. It is to monitor any soil movements or any changes in soil stress condition around the excavation zones and also the behaviour of retaining system and adjacent properties during excavation to ensure the safety of excavation and satisfactory performance. Proper planning of instrumentation program and qualified interpretation of monitoring results by competent geotechnical engineer are essential in ensuring the effectiveness of the monitoring system, the accuracy/validity of the monitoring results and proper action in preventing possible damage. The knowledge and experience in common type of instrument are the successful for safety control in underground basement construction works, Table 2.1.

14 Table 2.1 [8] : Common types of instrument for basement construction works.

Types Groundwater Table/ Piezometric Pressure

Instruments

Purposes

Water Standpipe

Change level

Piezometer

Change in piezometric level

Consolidation settlement, uplift or weakening of soil

Lateral movement

Inclinometer

Lateral ground movement and deflection of retaining walls

Instability of retaining system and adjacent structures

Stress/Load

Vibrating Wire Stain Gauge Load Cell

Stress along strut member

Over-load of struts

Bar Stress Transducer

Stress in rebar of concrete retaining structure

Over-load of reinforcing bars

Earth Pressure Cell

Earth pressure distribution on retaining wall

Over-stress of earth retaining wall

Surface Settlement Point

Ground surface settlement

Movements of surrounding ground and damage to existing utilities

Building/Utility Settlement Point Settlement Gauge

Settlement of adjacent building and utilities Continuous settlement of Structures

Instability of structures

Heave Gauge

Elastic heave in soft clay

Soil weakening and instability of excavation

Extensometer

Vertical ground movements in various depth zone

Deep ground movements

Automatic Tunnel Monitoring Device

Movement of MRT tunnels

Ground heave, subsidence and lateral movement

Tiltplate/Tiltmeter

Tilting of structures

Instability of structures

Crackmeter

Cracks on structure surface

Uneven settlement of structures

Vibration sensor

Vibration effect to adjacent properties

Disturbance to foundation soils and structures

Settlement /Heave

Settlement /Heave

Tilt/Crack

Vibration

in

groundwater

Related Problem Seepage and subsidence

ground

Axial load of strut

15 2.2.3

Supervision and Construction Control

A competent Resident Engineer is required for site supervision and construction control. The work methodology through conceptual sequences in stages at various types of basement construction works is significant important for monitoring purposes. It contributed the unexpected circumstances can be predicted at early stage and recurrence of same incident can be immediately reduced or eliminated. A few methods of conceptual deep basement works in tall building have been practicing, however the most significant types work adopted in modern practice in Malaysia are as follows:1.

Open excavation with slope protection or with braced wall

2.

Closed excavation with braced wall.

Figure 2.5 : Open excavation with slope protection

The open excavation concept as Figure 2.5, is classical method implementing in tall building. It is generally carried out in wide area where surround is not constraint. The cost operation is not expensive, however construction period needs longer time to complete mainly due to earth excavation activity.

16

Figure 2.6 : Open excavation with braced wall (a) internally strutting to wall, (b) wall with ground anchor

In town and congested area, open excavation in deep basement is able to be carried out. However, permanent wall supported with bracing and anchor is required, as shown in Figure 2.6. The cost induced by the bracing system is expensive.

Figure 2.7 : Closed excavation with braced wall in full top down method

In constraint working area, execution of full top down method as shown in Figure 2.7, with closed excavation enable the substructure work in deep basement and building

17 superstructure can be concurrently constructed without obstruction. This method is look viable when the building required early occupying. However, more heavy machineries are required made cost incurred in basement work has been proof not economical compared with construction time.

Figure 2.8 : Semi top down work

In few occasional, in constraint working area, semi top down excavation is carried out for deep basement work. The conceptual method is hybrid of open excavation and top down method. It is illustrated as Figure 2.8

18 2.3

Bottom Up Method in Deep Basement

Bottom up method, refer to Figure 2.9 and Figure 2.10, is normally carried out in site area with fewer plant facilities to operate. In deep basement work, retaining wall structure is required. It may form permanent or temporary elements integrated with building structure. The excavation is carried out within the wall parameter. In absence of retaining wall structure, the excavation area is appeared bigger in size due to elimination of slope sliding. Generally, slope ratio is made 1 : 1.5 in vertical and horizontal respectively but subject to soil geology of the working area.

Figure 2.9 : Open excavation in deep basement work As the excavation proceeds, horizontal support using strut frame, bracing system or other shoring are to be installed in order to counteract the lateral pressure on wall due to

19 newly exposed cut [9]. Temporary appropriate dewatering provisions to suit geological or neighboring environment should be incorporated to keep the pit safe and free from the entering of ground water. The movement of soil in horizontal and vertical monitored using instrumentation gauges.

Figure 2.10 : Bottom up method in deep basement

Foundation rafts, pile caps or ground beam are constructed on base formation level. It is constructed from the lowest basement level up wards. The basements work is repeated until reach the ground level. The temporary strut and brace members are released and dismantled at suitable stages as the basements are completed gradually, then backfilling with suitable material is carried out until finished formation level.

20 2.4 Semi Top Down Method in Deep Basement Work

In urban area with congested, constraint adjacent building surround and complicated underground infrastructure, the bottom up method for deep basement work tall building is found not viable and cause more time spent merely contributed costly in money value. Semi top down method is looks more advantage as solution. In semi top down method, perimeter retaining wall structure is required at early stage. Generally, diaphragm wall or contiguous bored pile as retaining wall structure is more effective for deep ground. Temporary column usually at the same position of the permanent column and the form of steel stanchions as to support the basement structure is required to construct from the top level downward [9]. It always executed by inserting the steel stanchion in bored pile while concrete is still in green. The steel stanchion in bored pile is carried out at perimeter bay slab basement, as center portion remain to follow bottom up method.

Figure 2.11 : Lateral force acting in deep basement

21 In actual design, there is lateral force induced by earth pressure, hydrostatic and surcharge. The force acting on diaphragm wall is taken by slab as deep beam in horizontal then transferred to vertical steel column. The vertical steel column shall be designed in such away that able to eliminate the lateral force action. It is shown in Figure 2.11

Figure 2.12 : Semi top down work in deep basement

Casting work is starting from perimeter bay ground slab level as to form diaphragm action to support perimeter retaining structure, refer Figure 2.12. Excavation is performed from center portion of building downward. The intermediate temporary strut or bracing system is optionally constructed where it is required. The next below basement is cast and excavation carried out similarly. The process is repeated until reaching the required level at base formation where raft foundation, pile caps and

22 ground beams are constructed. The temporary column is encased and cast to form permanent column. Temporary dewatering system is provision to keep site free from underground water. The movement in horizontal and vertical is monitored using instrumentation gauges. The center portion of basement is constructed upwards using bottom up method. In general, there is no significant backfilling is required.

CHAPTER 3

METHODOLOGY

3.1

Introduction

A desk study is performed by establishment of data search methodology as shown in Figure 3.1. A well planned flow chart is drawn up in expectation that the requirements in study search will be no loop hole left out when search to be carried out from a study project. Time frame is set up for 14 weeks made to complete the overall study case from record compilation, assessment data, finding on analysis, conclusion/suggestion and project report write up is considered adequate in time.

3.2

Project Case Study

A few tall projects with basement underground within Kuala Lumpur area have been approached not only directly to main contractor and subcontractors on site but also directly consulting the project Client and consultants. Most of responses and feedback

24 from them are good. However most of those tall buildings are found with basement works have been earlier completed and documents compilation are inadequate for this study case. Among the inadequacies are the availability of documents is limited in term of authorization to access the compilation records, commitment and restricted approval due to company regulation within their organization; Client, Consultants and Contractors.

Figure 3.1 : Methodology flowchart of project study

Out of the projects approached, two projects are found have sufficient requirements for this study case. The selected projects mentioned, are based on criteria that underground basement work method meets the study case, accessibility and availability of project

25 data such as work methodology, photos, drawings, cost work and time planning from the

project

itself

and

contractor/subcontractor.

commitment

from

client,

consultant

and

main

CHAPTER 4

PROJECT 1 : BOTTOM UP METHOD IN DEEP BASEMENT WORK

4.1

Introduction

The project is located at Jalan Ampang, Kuala Lumpur, Malaysia. It comprises 3-storey basement which serves as underground parking area and 30-storey floors tower block for mixed development of hotel, residential and office floor.

The site is originally refurbishment of petrol kiosk with flatten platform. Neighboring buildings located adjacent to project, as shown in Figure 4.1, at west side is existing 6storey building and shop lot which foundations are supported on pile. At south-west side is 43-storey building with 3-basement founded on pile foundation and at south side is 38-storey building with 3-basement also founded on pile foundation. At north side is open ground parking area and at east is public road.

The building footprint is 5,163.75m2. The depth of basement excavation varied from 13m to 17m. Owing to the variation in subsoil condition and cost consideration, a

27 combined retaining system is adopted. The combined retaining system included open excavation with temporary closed berm slope protection using shotcreting, internal horizontal strutting with inclined-struts-and berm systems to support the earth retaining walls consisting of contiguous bored pile of size 750mm diameter and temporary sheet pile.

Figure 4.1 : Layout plan of retaining system

28 4.2

Substructure Construction Planning Sequences

The site geologically lies in the Kenny Hill residual deposits overlying Limestone Bedrock. A total of 12 number of borehole in soil investigation (SI) is carried out to identify the soil profile of the site. Geotechnical engineer has identified and confirmed that there is no limestone bedrock was encountered. In general, the site soil stiffness increases with depth based on Standard Penetration Test (SPT) value recorded from the SI. The raft foundation is adopted for the building. However, at center of building which houses lift core area, integrated bored pile with raft foundation is designed for construction.

The bottom up excavation for sub-structure basement is adopted by considering the availability of local expertise in open excavation work in using fewer plants to operate. The soil and structure behavior monitored to confirm the safe excavation works during basement construction are assured. The site observational method proposed by Ikuta et.al [10] as shown in Figure 4.2 is used to modify and optimize the retaining wall system. It is used to revise and confirm the design assumption and to predict the precise behaviour of the subsequent stages.

29

Figure 4.2 [10] : Site observation method chart

30

Figure 4.3 : Basement work planning in stages

The basement work is planned for construction in stages as shown in Figure 4.3. The work methodologies approached are based on sequences of planning work as below. a.

Erection of contiguous bored pile

b.

Foundation bored pile

c.

Earth excavation

d.

Instrumentation and monitoring

e.

Raft Basement Construction

f.

Erection of Strutting and Bracing

g.

Construction basement floors to ground level

h.

Backfilling with suitable material

31 4.3

Erection of Contiguous Bored Pile

Contiguous bored piles (CBP) retaining wall is adopted. The CBP construction work is carried out along building perimeter boundary at location as shown in layout plan in Figure 4.1. Progress work of CBP retaining wall is shown in Figure 4.4. The permanent reinforced concrete skin wall is cast in-situ integrated to contiguous bored pile as a better finish and water tight structure for basement area.

Figure 4.4 : Contiguous bored pile at perimeter site boundary At the side of project which is parallel to open ground parking area and Jalan Tun Razak, bare open excavation is carried out. However in restricted space area, a low temporary cantilever wall is adopted during the basement excavation.

32 4.4

Foundation Bored Pile

Based on soil properties at lift core, bored pile foundation is recommended by geotechnical engineer. It is integrated with thick raft foundation. The load at the area is high compared with other portion. The design load consideration is induced by lateral force as well as gravity load.

Figure 4.5 : Foundation bored pile in dry condition

The drilling work is carried out in dry hole, as shown in Figure 4.5. No bentonite agent to strengthen soil wall in the hole is required. All piles at the area are designed mainly in friction capacity more than end bearing capacity. The depth of piles from raft bottom

33 base is 6m and rock socket is not required. It is only 45 nos. of bored pile have been installed as design requirement at lift core area.

4.5

Earth Excavation

The excavation work needs proper planning to avoid time waste which contributing to cost and to control slope stabilization in safety aspect. It has been carried out in stages as shown in Figure 4.6.

Figure 4.6 : Excavation work in stages

The access to and from site has been made in gentle slope to enable transporting earth and sand carried out without disruption. Proper silt trap to discharge water out off site is

34 located at one place. A few temporary earth drain streams are adjusted to suite site ground water condition to flow water to the silt trap.

As excavation proceeds further down, the contiguous bored piles retaining wall is exposed further and left the upper part acting as cantilever. At the open cut area, the slope is stabilized with cut berm as to follow design requirement. The run off water at surface is protected from penetration into the slope by ensuring the exposed slope covered up with shotcrete, otherwise failure due to erosion may occur. It is shown in Figure 4.7.

Figure 4.7 : Exposed slope with shotcrete During the excavation work, ground water is kept pumping out of the excavation area by providing earth drain and sump. The location of silt trap sump and earth drainages system is not fit at one place. It is flexible and subject to progress of excavation work as shown in Figure 4.8.

35

Figure 4.8 : Progress of excavation work Excavation is completed when it is carried out reaching to require level in both bottom base of raft and lift pit. The base is then trimmed to proper required level, as shown in Figure 4.9 and laid with lean concrete.

36

Figure 4.9 : Proper trimming work at base

4.6

Instrumentation and Monitoring

A comprehensive instrumentation and monitoring adopted in construction of retaining wall is to ensure the performance of the retaining and basements structures as envisaged in the design. Main important instrumentation is inclinometer. The typical detail inclinometer is shown in Figure 4.10.

37

Figure 4.10 [8] : Typical installation details for inclinometer

A numbers of inclinometer are installed within the sheet pile behind retaining wall as shown in Figure 4.11. It is to monitor retaining wall and ground movement. The standpipe piezometers are installed behind the wall to monitor the groundwater level.

38

Figure 4.11: Installation Inclinometer behind wallperimeter bored pile

Data collected are verified to design assumption as to ensure that the effects of the construction on adjoining structures are minimised. The soil and structure behaviour are often monitored to confirm that the safety of excavation works during construction are assured. There are advantages to use monitoring data to optimize the design with backanalyses of excavation made during construction.

4.7

Raft Basement Construction

Reinforcement rebars are laid on lean concrete. Mechanical water pumps are kept working 24 hours daily. The base is ensured free of underground water. The

39 sequence in basement casting should be given priority from the deepest area as shown in Figure 4.12. Lift core area with lift pit sump is earlier cast, later it is used as sump to cumulate underground water flow in and discharge off site.

Figure 4.12 : Rebar installation for raft base in progress

Since casting is to be carried out in bulk concrete, pump concrete is used. It is shown in Figure 4.13. The output of concrete pump, based on site experience with normal site congestion and traffic in Kuala Lumpur, is approximately 25m3/hour. For massive quantity of concrete, low heat concrete is used. The slow hydration reaction in low heat concrete is able to reduce and even eliminate crack.

40

Figure 4.13 : Raft foundation concreting work is being in progress

Curing is kept to minimum seven days using polystyrene sheet cover on top surface as shown in Figure 4.14. At the expose side of raft foundation, chemical spraying curing is applied. Temperature is measured in raft foundation using thermocouple at different level of height. The differential temperature of raft foundation and ambient temperature is monitored and it should within allowable limit as design code of practice requirement.

41

Figure 4.14 : Raft foundation curing with polystyrene sheet cover on top surface.

4.8

Erection of Strutting and Bracing

The inclined-struts-and-berm system is introduced and two rows of inclined strutting are proposed. The support of inclined struts is designed as reinforced concrete corbel and integrated with raft foundation [11]. The typical illustration shall be referred to Figure 4.15.

42

Figure 4.15 : Typical installation of temporary inclined steel strutting structure with reinforced concrete corbel support integrated to raft foundation

The site is first excavated with temporary berm to foundation level for the construction of raft foundation. After completion of the raft foundation, the first row of inclined prop is installed followed by partial excavation at the earth berm for the installation of the second level of strutting. The last part of the earth is removed upon the installation of the lowest row prop. Figure 4.16 shows the constructions of inclined-struts-and-bermsystem and excavation work.

43

Figure 4.16 : Temporary strutting structure and excavation work in progress The temporary strutting work is adopted to prop contiguous bored and sheet pile. It is shown in Figure 4.17.

Figure 4.17 : Temporary strutting structure to support retaining wall (sheet pile and contiguous bored pile)

44 4.9

Construction Basement Floors to Ground Level

Construction of basements is carried out in stages. Work planning is more concern on progress with required capacity of concrete volume which able to be achieved. The sequences of casting until construction joint is planned to avoid disruption and clashing of consuming tower on site, refer Figure 4.18. Any rebar lapping provided shall be at engineer requirement and proper planning rebar bending schedule able to reduce rebar waste simultaneously. Normally, core wall is maintained constructed three to four floors above floor level.

Figure 4.18 : Basement floors in sequences casting work

The basement raft foundation shall be cast at required construction joint, refer Figure 4.19. Once the retaining wall integrated with basement floors completed with casting

45 and concrete is already achieved required strength, the temporary steel strutting and bracing are dismantled. Any opening on wall or slab due to access of dismantled strutting column or beam is then cast subsequently.

Figure 4.19 : Basement work at construction joint

4.10

Backfilling with Suitable Material

Upon completion of basement floor to ground floor, backfilling with suitable earth is required to cover up gap between basement floor wall or retaining wall and exposed slope. It is to form the base of road and drainage as shown in Figure 4.20.

46

Figure 4.20 : Gap between basement wall and open slope

The backfilling work shall be carried out in layers and compact properly to fill any void and hole behind the wall as shown in Figure 4.21. Normally sand is used. Sand backfilling method can be either with direct pour and compact using compactor or using pressure pump and water then compact using compactor. The base formed shall be monitored and any further minor settlement compared to required level shall be touch up later.

47

Figure 4.21 : Backfilling to required level

CHAPTER 5

PROJECT 2 : SEMI TOP DOWN METHOD IN DEEP BASEMENT WORK

5.1

Introduction

The project is located at Jalan Tuanku Abdul Rahman, Kuala Lumpur, Malaysia. It comprises 3-storey basement which serves as underground parking area and 30-storey floors tower block for mixed development of hotel, office floor, training center and business center.

The site is originally located 8-storey building which has been demolished. Neighbouring buildings located adjacent to project, Figure 5.1 shows that at west side is existing 26-storey building with 3-basement founded on pile foundation. At northwest side is 27-storey building with 3-basement founded on pile foundation and at north is 32-storey building with 3-basement also founded on pile foundation. At south side and east side are public roads. There is an existing 600mm thick diaphragm wall facing to existing 26-storey building at the west side.

49

Figure 5.1 : Layout plan of semi top down site

The building footprint is approximately trapezium shape at area of 4,925.43m2. The depth of basement excavation varied from 12m to 17m. Since the building is to be built at constraint area couple with limestone subsoil underneath, semi top down method is adopted. The contiguous bored pile of size 750mm diameter is built surround perimeter boundary attached to the existing diaphragm wall. The top down area is executed at perimeter bay and at center is executed with bottom up method. Thus, bracing work and backfilling work are able to be eliminated.

50 5.2

Basement Construction Planning Sequences

The site geologically lies in the Kenny Hill residual deposits overlying Limestone Bedrock. Cavity area is expected within the site. Thus, every column point has been earlier carried out with SI to identify soil properties and underground limestone bedrock. Foundation is designed to use bored piles at specified depth based on the SI integrated with 2.2m thick raft foundation

Figure 5.2 : Basement work planning in stages

The work sequences are shown in stages as Figure 5.2 above. The basement work is carried out with site observational method as in Figure 4.2 to modify and optimize the retaining wall system. It is used to revise and confirm the design assumption and to predict the precise behaviour of the subsequent stages. The work methodologies in semi top down method are listed below. a. Erection of contiguous bored pile b. Foundation bored pile c. Pre-installation of column stanchion d. Top down work

51 e. Excavation f. Bottom up work

5.3

Contiguous Bored Pile

The perimeter wall is required surrounding the boundary. In choosing the type of retaining scheme, the following factors are taken for considerations [12]. a. the site constraint b. the condition of the soil/ground, total excavation depth and area. c. The control on ground movement d. The importance of water tight as the location of ground table is high. e. The availability of machines and contractor’s experience in the local market to construct the proposed structures f. The construction feasibility, monitoring and control during construction After considering the factors as listed above, contiguous bored pile (CBP) size 750mm diameter is found feasible as the basement retaining system and adopted. Each CBP is carried out from existing ground level and end length approximately 2m depth anchored into sound rock. It is carried on perimeter boundary attached to existing diaphragm wall as shown in Figure 5.3.

52

Figure 5.3 : Contiguous bored pile work in progress CBP are cut to required level with reinforcement rebar, as shown in Figure 5.4, are left protruded. Capping beam is constructed on top of CBP to cap all CBPs together.

53

Figure 5.4 : Cut off contiguous bored pile to required level

5.4

Foundation Bored Pile

In preliminary soil investigation (SI) and history of adjacent building development in previous work, it is recorded that limestone area is laid within range of cavity underground. Geotechnical engineer has advised that every column foundation should have proper SI to be carried out on column location directly. There are five SI machineries have mobilized to site area for SI works. The intensive SI works, as shown in Figure 5.5, have been carried out prior bored pile work can take placed. The record,

54 analysis and result of the SI are used to finalize the length of bored pile should be bored. Each completed SI hole is then grouted up to original ground level.

Figure 5.5 : Soil investigation (SI) works are being in progress at each column position. The varies bored pile ranging of 1000mm φ to 1800mm φ are designed based on column load capacity. It needs to be rock socketed at minimum total length of 7 x pile diameter. The pile lengths are varies from 35m depth to 47m depth from ground surface. The ground water is recorded at average of 6m to 10m depth from existing ground level. Bored pile works are carried out in wet hole, as shown in Figure 5.6. Each hole is required temporary steel casing to be used for 12m depth. Bentonite to strengthen soil wall in the hole is need to be used.

55

Figure 5.6 : Lowering down rebar cage in wet hole bored pile

A total of four bored pile machines with two lifting cranes are used in this work. When bored hole completed, the reinforcement rebar cage is lower down and it is ready for concreting. Casting work is carried out at night time. Concrete tremie II is used for underground concreting in presence of underground water. The cut off pile level is measured to projected 1000mm above raft base.

56 5.5

Pre-installed Column Stanchion

Steel used as stanchion column in this project is universal column (UC). In design, the column stanchion is analyzed on the capacity to withstand primary horizontal and vertical loads during excavation works. Most of the steel column is installed at column point and later will act also as permanent column.

Figure 5.7 : Pre-installed steel stanchion column in bored pile The stanchion installation method is usually selected by the piling contractor. The method adopted is based on the installation depth, size of stanchion and size of bored pile [13]. The pre-concreting method is used in this project. The sequence installation of steel stanchion column in bored pile is illustrated in Figure 5.7 above. In this method, steel stanchion is installed after completion of drilling work and lowering of pile reinforcement. Then, concrete is poured until cut off pile level. The guide frame located on top casing of bored is used to position steel stanchion vertically. It is important in achieving positional accuracy.

57 5.6

Top Down Work

The excavation is carried out to required level for scaffolds stand on ground base to support ground beam and slab formwork, as shown in Figure 5.8. The protruded stanchion column is ensured securely joint to floor slab by providing welded square steel plate. The slab reinforcement is lapped on top and bottom of the steel plate. At steel stanchion column, rebar is welded with allowable lapping length into slab.

Figure 5.8 : Ground floor formwork in progress Excavation is carried out simultaneously to lower basement from center area. The disturbance to cast area should be definitely avoided. Once, the cast ground floor has sufficient concrete strength, the formwork is dismantled. The construction of top down is carried out at the perimeter building where the area is pre-installed with steel stanchion. Column with steel stanchion used as permanent column, need to properly

58 clean from soil. The reinforcement rebar using mechanical coupler is used to joint both top and bottom ends, refer Figure 5.9. Later, formwork is fabricated and the column is cast as usual as in normal practice.

Figure 5.9 : Top down work in progress The basement excavation work is carefully carried out. At early stage, heavy excavators are operating from ground slab area, as shown in Figure 5.10. As such, the perimeter slab is designed to take loads of accommodating heavy machineries and trucks on it. The slab thickening and more reinforcement rebar than normal are among parameter required in the slab and beam during construction period which is designed as permanent element.

The exposed steel stanchion column should be cleaned and free

from any agent which protected concrete from bonding to it.

59

Figure 5.10 : Excavation work to expose pre-installed steel stanchion column As the excavation has to go down deeper and deeper, excavators required for excavation are directly located on basement area. In this project as shown in Figure 5.11, three excavators are placed at the basement for ground excavation work. From the open area, the excavator needs to enter the underneath top down area which completed with cast slab and beam for earth excavation work. The tendency of excavator arm to hit beam and slab soffit at the area is very large. The work has to be performed in safely and carefully manner. When the excavation reached to second basement area, ground water starts to come out from the ground. The temporary of earth drains and sump are needed to be established immediately. Mechanical pumps at sufficient capacity are provided at sump area. Any contamination in water should be filter through silt trap. As authority requirement, clean water is discharged out of area into the nearby surface drain to the river.

60

Figure 5.11 : Excavation work to formation level carried out at center of building downward. One excavator, operating from ground slab is accommodated with long arm shover. It has to take earth from the bottom basement and load into the truck at ground slab area. The process of excavation is continuously carried out until all earth have been excavated to form raft base at required level

5.7

Floor Casting and Top Down Work

The floor casting is identified by dividing the area into zones. Each zone is terminated at pre-installed steel stanchion column by forming construction joint. The

61 concrete of each zone is ensured adequate to be handled for approximately 6 to 8 hours per casting activity at night time. Otherwise construction joint has to be immediately rescheduled form for the next casting work.

Figure 5.12 : Top view of top down work at perimeter building As shown in Figure 5.12, all perimeter zone areas from ground level downward to raft foundation are carried using top down method. No bottom up structure is designed to be simultaneously constructed on perimeter area during the top down work in this project. The column at top down area has been analyzed and designed to execute loading induced in ground floor to basement activity only.

62 5.8

Foundation Base Casting and Bottom Up Work

At center area of building, once the excavation has reached raft base, lean concrete is laid to make working area neat and clean for reinforcement rebar work. Ground water is avoided to enter the working area by ensuring sump is constructed at nearby area. Temporary earth drain is built and ground water is ensured flow along it by gravity into to the sump. The water is discharged out of site using mechanical pumps which are kept running continuously.

Figure 5.13 : Bottom up work at center of building As shown in Figure 5.13, rebar work for the raft foundation at bottom up area is fabricated until construction joint. The special joint for raft base is designed to have water stop. The jointing method of water stop at the area is carried out according with

63 specialist advice and follow technical requirement from manufacturer. Reinforcement rebar is ensured left spanning outside from face of construction joint area at required lapping length for subsequent casting. Formwork is fabricated at construction joint face in both vertical and horizontal alignment props. The strengthening to the formwork prop is required whenever raft depth cast is too high. However, in this project, the thickness of raft 2.2m is considered normal and generally use in construction practice in Malaysia.

Figure 5.14 : Bottom up area with basement raft work in progress

At columns point where pile foundations are used, lapping from bored pile reinforcement rebar with sufficient length is anchored into raft base. Beams are cast

64 homogeneously with the raft and also act as tie beams spanning from column to column, as shown in Figure 5.14. At slab area, since the thickness of raft is 2.2m, the top rebar is required to hold in its upper position on support rebar chair which specially designed to ‘U’ shape. Concreting in massive quantity is continuously cast using pump method. It is properly poured in order to avoid occurrence of cold joint.

Figure 5.15 : Bottom up work for center building structure

Upon completion of raft foundation at lowest base, columns, shear walls, lift core walls and skin wall at perimeter building which located at basements are cast bottom up. As normal bottom up working activity in vertical elements, reinforcement rebar are installed to its position then formwork is fabricated to required size. In this project,

65 since it is located in town area, casting is inevitably carried out mainly at night time. The process of bottom up method at the center portion of this project is carried out until ground level and further upper for superstructure work until roof level as shown in Figure 5.15.

CHAPTER 6

DATA ANALYSIS

6.1

Introduction

All data collected from both of bottom up excavation method and semi top down method on field study required for objective of this project report are properly compiled. The proper attention are given to followings aspects in view of construction considerations with sound understanding in design of underground work, a) Tabulation of parameter activities b) Design consideration should take place during activity work c) Time and cost taken to complete each activity.

67 6.2

Parameter Activities

The deep excavation work in underground basement has been mostly influenced by work methodology itself. Data are collected by recording all circumstances incurred during the work. The comments and advices from both consultant and contractor are information encountered during work being carried out. It needs to be recorded and compared with earlier predictable element during design and planning work. The tabulation parameter of bottom up construction method is listed in Table 6.1, meanwhile semi top down method is in Table 6.2

6.3

Design Parameter

The site observation method adopted in both basement works is used by geotechnical and structural engineer to analyse result on field work. The analysed results are then used to satisfy the assumptions envisaged in design office, otherwise the revised design is required immediately. The summary of basement work activity from both methods is tabulated. The awareness of the activity monitoring in any circumstances has enabled both geotechnical and structural designers classified what to do rather than depends solely on contractor trial on error work on site. In actual site work, the excavation work caused most others parameter changes simultaneously in presence with underground water. Ground movement may contribute vertical and horizontal deformation in retaining structure element. It causes more problem arises when the next course of action late to resolve. The forecast problem such

68 as slope erosion and collapse should be monitored closely by Resident Engineer. With the presence of tabulated parameter as shown in Table 6.3, Resident Engineers are easily identified the right person to consult, subsequently coordination with all parties concerned is able to hold in order to resolve whatever matter arised smoothly.

69 Table 6.1 : Parameter in bottom up excavation method in underground basement work Item

Activity

Description

Comments

1.

Foundation

Bored Pile and Raft Base

•

Pile foundation integrated with raft foundation based on underground soil properties to reduce differential settlement.

2.

Retaining structure

Contiguous bored pile and reinforced concrete skin wall

•

Form part of building structure at parameter building adjacent to existing building from basement up to ground floor.

3.

Excavation

Open excavation with shotcrete slope protection. At localized area with stiff slope need temporary sheet pile.

4.

Dewatering work

Temporary silt trap and earth drainage/sump

• •

• •

5.

Strutting and Bracing

Temporary work propping to retaining wall structure.

•

•

To avoid excessive erosion and collapse to exposed slope. Sheet pile installed at toe slope by maintaining open cut slope with shotrete protection on exposed surface. To discharge underground water from basement working area To ensure base is free of water at concreting work area. Acting as temporary structure and dismantle upon completion of basement. To ensure retaining wall structure capable to retain lateral forces due to adjacent building load, hydrostatic pressure and surcharge during excavation work.

6.

Instrumentations

Inclinometer, piezometer, and tiltmeter

•

To monitor the horizontally, verticality structure levelling and underground water table during construction work

7.

Concreting

Basement structure concreting work

•

To cast all column, beam, slab, core wall, skin wall etc which at basement area

8.

Backfilling

Backfilling with suitable material

• •

To cover up all open excavation at exposed slope to form base for road and drainage work

70 Table 6.2 : Parameter in semi top down method in underground basement work Item

Activity

Description

Comments

1.

Foundation

Bored Pile and Raft Base

•

Pile foundation integrated with raft foundation based on underground soil properties to reduce differential settlement.

2.

Retaining structure

Contiguous bored pile and reinforced concrete skin wall

•

Form part of building structure at parameter building adjacent to existing building from basement up to ground floor.

3.

Stanchion column

Pre-installed column

•

Install during piling foundation work in bored pile and formed as permanent column. Able to take vertical and horizontal load by ensuring basement floor slab acting as diaphragm beam transferred load to it during basement work

steel

•

4.

Excavation

Basement excavation

•

Excavation performed from the center of building downward to basement.

5.

Dewatering work

Temporary silt trap and earth drainage/sump

•

To discharge underground water from basement working area To ensure base is free of water at concreting work area.

• 6.

Instrumentations

Inclinometer, piezometer, and tiltmeter

•

To monitor the horizontally, verticality structure levelling and underground water table during excavation work

7.

Concreting

Basement structure concreting work

•

To cast all column, beam, slab, core wall, skin wall etc which at basement area

Stanchion column

Earth excavation

Slope protection/shotcrete

Temporary strutting/bracing

Instrumentations

Temporary dewatering system

Backfilling with suitable material

3.

4.

5.

6.

7.

8.

9. •

•

•

•

•

•

•

•

•

to form base for road, drainage and ground area with allowable degree of compaction.

to ensure site free from underground water and influence ground settlement.

site monitoring gauges to monitor deformation in vertical and horizontal during excavation work.

steel structure to prop retaining wall formed by sheet pile or contiguous bored pile.

designed to stabilise slope from erosion and collapse.

designed at allowable slope and berm gradient.

designed to withstand vertical and horizontal force at preliminary work and anchorage into pile foundation.

√

√

√

√

√

√

√

√

Depend on soil properties and designed to transmit loads into hard strata underneath. Take lateral and vertical forces. Designed to counteract loads induced from neighbourings buildings and surcharge.

BUM

REMARKS

√

√

√

√

√

√

STDM

√

√

√

√

√

√

√

√

√

√

√

√

√

STRUCTURAL DESIGN INVOLVEMENT STEEL R.C GEO.

√ = applicable, BUM = Bottom Up Method, STDM = Semi Top Down Method, R.C = Reinforced Concrete, GEO = Geotechnical

steel

Retaining structure

2.

wall

Foundation

ACTIVITY

1.

Item

Table 6.3 : Parameter designs influenced in bottom up and semi top down method of underground basement work

71

72 6.4

Time and Cost Completion Activity

In both methods, refer Table 6.4 and Table 6.5, costs at completion of basement work are based on specialist price which mean from direct local sub-contractors of these two projects. The main contract cost of project is not viable to consider since Project 1 is under private development meanwhile Project 2 is under government development. Thus it is not under the same development case. Pile foundation activity in both projects should not be considered influenced the basement work activity in construction stages as it is able to be carried out independently. Determination of the use bored pile as foundation is designed solely based on soil properties. It is to transfer building loads vertically to hard strata underneath. In Project 1 which basement works are carried out by bottom up method, the building foundation is designed as raft foundation. However, pile foundation of 45 nos. bored pile is designed to support core wall which located at center of building. Core wall is designed as main braced element in tall building as to take both forces from lateral wind load and vertical (gravity) building load. By referring Table 6.4, with absence of pile foundation activity, the basement work completion is still remains at 392 days. Hence, total completion cost should be RM 9,646.800.00 − RM 565,000.00 = RM 9,081,800.00 . The footprint area Project 1 is 5,163.75m 2 . Thus, based on working area for three stories basement work, the cost rate is

RM 9,080,800.00 RM 1,758.76 = 5,163.75m 2 m2

Meanwhile in Project 2 which basement works are carried out by semi top down

method, the pile foundation is designed as building foundation. As to simulate the costing of basement work, the costing of Project 2 by referring Table 6.5, should be

73 assessed in absence of pile foundation. The time still remains at 303 days to complete the

basement

work.

Hence,

total

completion

cost

is

RM 10,418,500.00 − RM 2,750,000.00 = RM 7,668,500.00 . The footprint area Project 2 is 4,925.43m 2 . Based on working area for three stories basement, the cost rate is RM 7,668,500.00 RM 1,556.92 = 4,925.43m 2 m2

Figure 6.1 : Actual cost and time completion for semi top down method and bottom up method without pile foundation

The analysis of cost and time of both methods is tracked from operations in Table 6.4 and Table 6.5. It is superimposed into one graph as shown in Figure 6.1. From the graph, at the first of starting project until 3.8 months, cost operation of both methods is likely same. However for the period of 3.8 months to 7 months, the operation cost of

74 semi top down method is seems less than bottom up method. Contrary, at the 7 months towards 10 months i.e at the end of completion progress of semi top down method, cost operation of semi top down method is seen more than cost operation of bottom up method. However, semi top down method is finished three months earlier than bottom up methods with less cost.

Table 6.4 : Actual work completion of bottom up method for Project 1

75

Table 6.5 : Actual work completion of semi top down method for Project 2

76

CHAPTER 7

CONCLUSION AND SUGGESTION

7.1

Introduction

In tall building with underground basement, completion on time is one critical item vital to the owner, the consultants and the contractor. Close coordination and cooperation between all parties concerned, together with the use of latest technique and a reliable and diligent workforce had ensured the completion of the building on schedule.

7.2

Conclusion

The justification for the both of semi top down and bottom up methods has been made in both 30-storey tall building with three basements construction for Project 2

78 which is commenced one year late from Project 1 based on field compiled data and analysis result.

Thus, the followings have been concluded, 1.

The work methodology and activity on site are depend on construction parameter which influenced both completion cost and time both method of basement works.

2.

Semi top down method requires simultaneously preinstalled column stanchion and retaining wall element.

3.

Elimination of strutting structure, earth backfilling work and shorten time in excavation work due to reduction in excavation volume, is seems influenced semi top down method completed work earlier with cost saving compared with bottom up method.

Eventhough, the cost rates in both project activities are based on present time of price from local expertise, semi top down method has given more benefit in term of reduction construction time and competitive cost saving. However performance in each activity is solely depend on reliable local expertise with availability of modern equipment and machinery to carry out the underground basement work.

7.3

Suggestion

. In tall building with underground basement, the effectiveness and suitably method of construction to carry out basement work is needed to study from a few similar projects within same type of geological area. The construction cost budget in

79 three basements underground of tall building to be built is related to time completion of each project which mainly contributed by method in work implementation. In feasibility study, cost and time referred should be based on records of completed project within the same conceptual designed and work method. Based on field study which is carried out from these two projects, the rate of construction time and rate cost at subcontractor price is suggested for preliminaries study in three basements work of tall building could be summarized as below, 1.

Rate of completion time for semi top down method is 16.3m2/day and for bottom up method is 13.2m2/day.

2.

Rate of construction cost at sub-contractor price for semi top down method is RM 1,556.92/m2 and for bottom up method is RM 1,758.76/m2.

The above suggestion is exclusive of pile foundation contribution.

80

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3. Narong Thasnanipan, Aung Wing Maung & Pornpot Tangseng (2006), Important of Temporary Works and Construction Sequence – Lessons from Collapse of an Inlet Shaft During Excavation, International Symposium on Underground Exacavation and Tunnelling, 2-4 February 2006, Bangkok, Thailand from http://www.itaaites.org/cms/fileadmin/filemounts/general/pdf/ItaAssociation/Organi

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81 11. Lim, C.S., Tan, S.M. & Hiew, L.C. (1999), A Basement Excavation Using Tie Back, Internal Horizontal Strutting and Inclined-struts-and–berm system, SSP. Geotechnics Sdn. Bhd, Selangor Darul Ehsan, Malaysia from www.sspsb.com.my 12. Sofiana Talha (2000), Deformation Behaviour of a Retaining Wall for a Deep Basement Excavation with Semi-Top Down Method, SSP Geotechnics Sdn. Bhd, Selangor Darul Ehsan, Malaysia from www.sspsb.com.my. 13. Narong Thasnanipan, Aung Wing Maung & Zaw Zaw Aye (2000), Practical Installation of Stanchion For Top Down Construction in Bangkok Subsoil, Development in Geotechnical Engineering, Thailand, pp 337-346 from www.seafco.co.th/RDpaper/BP-10.pdf.